Portable power equipment, such as snow blowers or similar apparatuses, typically use hydrostatic transmissions (HST) to operates. Due to cavitation within the HST, the HST loses efficiency due to air bubbles generated by the turning of the gears, particularly when the air bubbles get trapped in the check valve seats of the hydraulic circuit. Therefore, there is a need to prevent make-up oil entering through the check valve seats to be free of cavitation air bubbles.